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  <title>Document</title>
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  <script>
    console.log( isNaN('qwer') )  // true

    console.log( isNaN(111) )  // false

    // 隐式类型转换：  '123' =->  123
    console.log( isNaN( '123' ) )  // false

    console.log( isNaN( 'A123' ) )  // true


  </script>
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